01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving overhang on two sides for easy removal.
02 - In a heatproof bowl set over a saucepan of simmering water, melt the butter and chopped dark chocolate together, stirring gently until completely smooth. Remove from heat and let cool for 5 minutes.
03 - Add both the granulated sugar and light brown sugar to the chocolate mixture. Whisk until fully combined and smooth.
04 - Add the eggs one at a time, whisking thoroughly after each addition until fully incorporated. Stir in the vanilla extract.
05 - Sift the flour, cocoa powder, and salt together directly into the batter. Fold gently with a spatula until just combined — do not overmix to keep brownies tender.
06 - If using, fold in the chopped nuts and/or dark chocolate chips until evenly distributed throughout the batter.
07 - Pour the batter into the prepared baking pan and spread evenly. Smooth the surface with a spatula.
08 - Bake for 22–25 minutes, or until the top is set and slightly crackly with a gentle jiggle in the center. Avoid overbaking for the best fudgy texture.
09 - Allow the brownies to cool completely in the pan on a wire rack. Once fully cooled, lift out using the parchment overhang and cut into 12 squares.